Grinding wheel for longitudinal or transverse grinding

ABSTRACT

A grinding wheel has an inner core part and an outer annular grinding part connected the inner core part. The outer grinding part is made of a granular abrasive medium and plastic or glass fibers. The fibers form between 0.15% and 1%, preferably 0.2% to 0.4%, by weight of the grinding part.

FIELD OF THE INVENTION

The present invention relates to a grinding disk or wheel. More particularly this invention concerns such a disk or wheel that can grind both longitudinally and transversely.

BACKGROUND OF THE INVENTION

A typical grinding wheel for longitudinal and transverse grinding has an inner core part and an outer annular grinding part that are connected to each other. The grinding part is made of a material that contains a granular abrasive compound. EP 1,129,824 discloses a grinding wheel of this kind.

When processing plate slabs in the manufacture of steel, the surfaces undergo abrasive machining to remove any faulty areas such as voids that may be present. A grinding wheel is used to this end containing particles in the abrasive compound thereof in the grinding part. The selection of the abrasive particles depends on the workpiece being machined. In most cases, abrasive particles should be very hard, with sufficient particle toughness and resistance to heat, as well as suitable particle sizes and shapes. Frequently used abrasive particles are made from carborundum (aluminum oxide), silicon carbide, cubic boron nitride or diamond, which grinding materials have been named in the order of ascending hardness. The shape of the abrasive particles as well as the particle sizes thereof depend on the type of machining, namely, whether so-called rough-grinding, pregrinding, finish-grinding or precision-grinding.

During the grinding process, the grinding wheel is rotated at relatively high speeds of 80 m/s or more. Considerable centrifugal forces are generated at such grinding speeds requiring high-level security measures. The relatively high susceptibility of the grinding wheels to breakage poses a risk for operators, as it can cause single large pieces of the grinding disk or even entire segments of grinding parts to detach. Despite necessary safety steps, namely by balancing the grinding wheel, sound testing before the start-up of operation, careful mounting of the grinding wheel and enclosing the grinding wheel inside a protective hood, the durability of the grinding wheel is of the utmost importance. In particular, any detachment of individual segments of the grinding part must be effectively avoided.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved grinding wheel.

Another object is the provision of such an improved grinding wheel that overcomes the above-given disadvantages, in particular that is very rugged and unlikely to come apart even if rotated at very high speeds.

SUMMARY OF THE INVENTION

A grinding wheel has according to the invention an inner core part and an outer annular grinding part connected the inner core part. The outer grinding part is made of a granular abrasive medium and plastic or glass fibers. The fibers form between 0.15% and 1%, preferably 0.2% to 0.4%, by weight of the grinding part.

Although the use of filler materials, including glass fibers, has been proposed previously for cutting wheels of smaller diameters or even for larger grinding wheels, in these instances, the goal was to minimize cost of the grinding wheel. The centrifugal force of a grinding wheel is calculated from the product of mass, square of the angular velocity and distance from the axis of rotation; this means that especially grinding wheels that have a large mass and a large diameter are subject to enormous centrifugal forces. Correspondingly, the formation of hair-line fractures that triggers the detachment of parts from grinding parts at a later time must be avoided. For this reason, strict adherence to the percentage parts of mass for plastic or glass fibers is required. The risk of breakage increases dramatically above 1.0 mass % of the grinding part. Below 0.3%, any addition of plastic or glass fibers is for the most part without effect at all. Only the restricted quantity of 0.15% to 1.0% in fact results in good adhesive power of the grinding wheel portions without compromising toughness.

Preferably, glass fibers of a length of 5 mm to 15 mm and a thickness of 0.8 mm to 1.2 mm are used.

The grinding wheels according to the invention have, for example, a standardized diameter of 615 mm with a thickness of 79 mm and an inner bore hole in the core part with a diameter of 203 mm. The outer diameter of the core part is 340 mm. The weight of such a grinding wheel, including any embedded iron reinforcement rings, is about 63 kg. To avoid any relative movement of the core and grinding parts in the direction of rotation, the substantially cylindrical outer surface of the core part is formed with individual grooves or singular recesses, and the cylindrical inner surface of the grinding part includes complementary individual ridges or singular bumps. The ridges or singular bumps engage in the grooves or singular recesses of the core part, respectively, to produce an effective “keying” between the core part and the grinding part. The corresponding grooves, recesses or bumps can be easily incorporated during cold shaping.

The present invention provides, in principle, for the use of all common grinding materials, preferably Al₂O₃, SiC, CBN, ZrO₂, diamond or mixtures of these material, the maximum particle diameter being no more than 1 mm.

As known, in principle, from above-cited EP 1,129,824 T2, the core part and the grinding part have the same thermal coefficients of expansion. If necessary, the coefficients of expansion can deviate by a maximum of 5% from each other. This measure ensures that, when the grinding wheel becomes hot during operation, differential stresses between the core region and the grinding part are for the most part avoided.

Aside from the abrasive particles, the core and grinding parts can principally be made of the same or different materials. According to a further embodiment of the invention, the grinding part can contain a matrix of metal or a metal alloy or a thermally curable resin in which the granular abrasive medium and the plastic or glass fibers are embedded in a homogenous distribution, at least for the most part homogeneously. The core part can substantially be made of metal and/or metal alloys that have filler materials added thereto, if necessary. In particular, it is possible to use the core part multiple times. Thus after the grinding part is worn out, what is left of the grinding part can be separated from the core part, and a new grinding part can be formed on the core part.

In particular with regard to at least approximately equal thermal coefficients of expansion, however, the core part (preferably the grinding part as well) can contain a thermally curable resin and a cross-linking agent as well as filler materials. Fillers can be, for example, powdery SiC, Al₂O₃, bauxite, graphite or molybdenum sulfide.

To be able to ensure optimum solidity of the grinding wheel, it is preferable to produce the core section first, followed by the cutting portion, by cold shaping. The green compact formed in this manner, which is made of the core and grinding parts, is already provided with grooves and ridges that engage with each other in the manner following a tongue-and-groove principle (or, in the alternative, singular recesses and singular pegs).

The combined compacted green compact is then heated to 180° C. to 200° C. and compacted to the desired final dimensions. The compression pressures are, for example, 7×107 Pa (700 bar).

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a top view of a grinding wheel according to the invention;

FIG. 2 is a side view of the grinding wheel; and

FIG. 3 is a section taken along line III-III of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

As seen in FIGS. 1 and 2 a grinding wheel according to the invention has an inner core part 10 and an outer grinding part 11, both centered on an axis A. The outer diameter of the grinding part measured diametrally is 615 mm and the axial thickness of the grinding wheel, as seen in FIG. 2, is 79 mm. Both parts 10 and 11 are, in fact annular, with the grinding part 11 outside the core part 10 so that the cylindrical inner surface of the outer part 11 is in surface contact with and bonded to the cylindrical outer surface of the inner part 10.

As shown in FIG. 3, a keyed connection can be created between the core part 10 and the grinding part 11 in that the core part 10 is provided with radially outwardly extending circumferential ridges 12 that engage in complementary radially inwardly open annular grooves 13 of the grinding part 11. Alternatively as shown in the left half of FIG. 3, there are individual bumps 14 and complementary recesses 15. Such projections or depressions are formed already at the time of production of the green compact by precompacting, such that the combined body, which is made of the precompacted core part and precompacted grinding part, is placed into a mold and subsequently heated to 180° C. to 200° C., then finally compacted to the above-given final dimensions.

According to the invention, aside from the matrix material in which are imbedded the abrasive particles made of, for example, aluminum oxide, the grinding part has a mass fraction of 0.15% to 1.0% of plastic or glass fibers 17. A concrete embodiment provides for the use of about 100 g glass fibers 17 of a mean length of 10 mm and a thickness of 1 mm for the core part 10 and the grinding part 11. The glass fibers 17 were homogeneously blended. The core part had a total weight of 12 kg, while the grinding part, on the other hand, had a powder weigh-in of 49.5 kg. Two additional iron rings 16 are also embedded in the structure and have a weight of 1.0 kg, resulting in a total weight of 62.5 kg for the grinding wheel. In the illustrated embodiment, the glass fiber fraction of the weight of the grinding part and the core part was approximately 0.17%, respectively.

The grinding wheel was inspected during a test run at rotational speeds of 140 m/sec; chipped spots on larger parts of the grinding part or hair-line fractures that can result in detachments later on were not found. Contrary to grinding wheels without glass fiber content, by the targeted addition of glass fibers 17 it is possible to achieve a considerable improvement in terms of the solidity of the grinding wheel. 

We claim:
 1. A grinding wheel comprising: an inner core part; and an outer annular grinding part connected the inner core part and comprised of a granular abrasive medium and plastic or glass fibers, the fibers forming between 0.15% and 1% by weight of the grinding part.
 2. The grinding wheel defined in claim 1, wherein the fibers form between 0.2% and 0.4% by weight of the grinding part.
 3. The grinding wheel defined in claim 1, wherein the fibers have a length of between 5 mm and 15 mm and a thickness between 0.8 mm and 1.2 mm.
 4. The grinding wheel defined in claim 1, wherein the core part has a substantially cylindrical outer peripheral surface formed with indentations and the outer grinding part has a substantially cylindrical inner peripheral surface engaging the outer surface and formed with projections complementary to and engaging into the indentations of the outer surface, whereby relative shifting of the parts at the surfaces is inhibited by inherit of the indentations and projections.
 5. The grinding wheel defined in claim 1 wherein the grinding wheel is made of particles of Al₂O₃, SiC, CBN, ZrO₂, diamond or mixtures thereof.
 6. The grinding wheel defined in claim 5, wherein the particles have particle sizes of a maximum diameter of 1 mm.
 7. The grinding wheel defined in claim 1 wherein the core part and grinding part have thermal coefficients of expansion that deviate from each other by less than 5%.
 8. The grinding wheel defined in claim 1, wherein the grinding part has a matrix of a metal or metal alloy or of a thermally curable resin in which is embedded granules of abrasive media and the glass fibers in a generally homogenous distribution.
 9. The grinding wheel defined in claim 8, wherein the core part is substantially made of a metal or metals and filler materials.
 10. The grinding wheel defined in claim 1, wherein at least one of the parts contains a thermally curable resin and cross-linking agents and fillers.
 11. The grinding wheel defined in claim 11, wherein the fillers are as SiC, Al2O3, bauxite, graphite or molybdenum sulfide.
 12. The grinding wheel defined in claim 1 wherein first the core part, then the grinding part are compacted by cold shaping to form a combined green compact that is heated to 180° C. to 200° C. and compacted to desired dimensions. 